1. Field of the Invention
The invention pertain to pulsed lasers, specifically to optically pumped solid state lasers. The present invention has particular application to optically-pumped lasers which include a plurality of laser rods and in which each laser rod is optically pumped at a level below its maximum output operation so that refrigeration cooling is not required.
2. Description of the Related Art
Many conventional solid state laser systems employ optical pumping means to excite solid state gain media into a lasing state. For example, in one type of conventional solid state laser system, the gain medium is a cylindrical rod, and the optical pumping means comprises elongated flash lamps positioned parallel to the rod. Radiation for optically pumping the rod is focused from the lamps onto the rod's central longitudinal axis. The rod and the adjacent flash lamps are mounted within a reflective housing. The entire assembly (comprising rod, flash lamps, and housing) is referred to as a "laser head."
Most solid state gain media in common use can be maintained at a relatively high temperature during lasing operation. However, some solid state gain media, such as Holmium:YAG material, Holmium:YLF material, and other Holmium-doped gain media, are preferably maintained at a low temperature during lasing operation (for example, a low temperature in the range from about +10 degrees Celsius to as low as about -15 degrees Celsius) for maximum power output. A cooling system is required for this purpose, since the flash lamps (or other optical pumping means) will otherwise increase the temperature of the entire laser head (including the gain medium) to undesirably high levels. Existing lasers use refrigerant cooling to achieve the range of temperatures specified above.
However, refrigerator-cooled Ho:YAG lasers have serious drawbacks. The cooling system typically is heavy, bulky, noisy, and expensive to fabricate. Also, there are problems in shipping laser systems with the typical water/alcohol refrigeration coolant.
Also, there are limits, even with refrigeration, on the rate at which a Ho:YAG laser can be pumped before the efficiency of the laser drops. Additionally, increasing the optical pumping rate and intensity runs the risk of damaging the Ho:YAG laser rod.